Polyethylene terephthalate foam and method for producing the same

Abstract

The present application relates to a kind of polyethylene terephthalate foamed materials and its preparation method, the preparation method includes the following steps: polyethylene terephthalate material is heat pressed, and the preform of molten state is obtained;The preform of molten state is treated with melt isothermal crystallization and quenching, and sheet material is obtained;And the sheet material is treated with foaming, and polyethylene terephthalate foamed material is obtained.The present application uses melt isothermal crystallization treatment, can improve the melt strength in the foaming process of polyethylene terephthalate, strengthens its foaming performance, simultaneously can also be realized by strengthening bubble nucleation and controlling bubble growth to adjust the bubble morphology of foamed material, so can obtain the polyethylene terephthalate foamed material of bubble size uniform and controllable foaming ratio.

Description

Technical Field

[0001] This invention relates to the field of foaming materials technology, and in particular to polyethylene terephthalate foaming materials and their preparation methods. Background Technology

[0002] Conventional industrial-grade polyethylene terephthalate (PET) has a linear structure, a small molecular weight, and a narrow distribution, which results in a low melt strength during the foaming process. The matrix cannot support the continuous growth of the cells, causing the foaming gas to easily escape, leading to cell aggregation and even rupture. This results in a poor cell structure in the foamed material, which seriously affects the application of PET foamed materials.

[0003] To improve the cell structure of PET foam materials, PET needs to be modified to increase its melt strength during the foaming process. For example, traditional techniques use terpolymers as foaming agents to enhance the melt strength of PET, resulting in high-performance semi-crystalline PET foam materials through extrusion foaming. However, chemical foaming agents are used in the extrusion foaming process, leaving some residue in the foamed product, affecting its performance and safety. Another example is the use of supercritical CO2 foaming to prepare PET foam materials. High-pressure CO2 dissolves a large amount of PET in the matrix, inducing crystallization and resulting in a nanoporous structure. However, the time it takes for PET to reach saturation equilibrium in high-pressure CO2 is as long as 30 days, posing significant challenges to equipment safety and experimental reliability. For example, traditional techniques use high melt strength LDPE to blend with PET to improve the melt strength and foaming properties of PET, and then prepare foamed materials through compression molding. However, this process requires the addition of compatibilizers, crosslinking agents, and foaming aids, making the operation complex and resulting in uneven cell distribution. Therefore, there is still a need to develop a simpler method for preparing PET foamed materials. Summary of the Invention

[0004] Therefore, it is necessary to provide a polyethylene terephthalate (PET) foam material and its preparation method to address the above problems. The preparation method can improve the melt strength of PET foaming process, and can also control the cell morphology of the foam material by strengthening cell nucleation and controlling cell growth, thereby obtaining a PET foam material with uniform cell size and controllable foaming ratio.

[0005] A method for preparing a polyethylene terephthalate foam material includes the following steps:

[0006] Polyethylene terephthalate material is hot-pressed to obtain a molten preform;

[0007] The molten preform is subjected to melt isothermal crystallization and quenching to obtain sheet material; and

[0008] The sheet material is foamed to obtain polyethylene terephthalate foam material.

[0009] In one embodiment, the isothermal crystallization process of the melt is carried out at a temperature of 230°C-245°C for a time of 3 min-40 min.

[0010] In one embodiment, the intrinsic viscosity of the polyethylene terephthalate is 0.6 dL / g to 0.8 dL / g.

[0011] In one embodiment, the quenching medium in the quenching process is selected from ice water or liquid nitrogen.

[0012] In one embodiment, the thickness of the sheet material is 0.5 mm to 3 mm.

[0013] In one embodiment, the step of foaming the sheet material is as follows: the sheet material is saturated by adsorption in a foaming gas to obtain saturated sheet material, and then the saturated sheet material is foamed in a foaming medium.

[0014] In one embodiment, the step of saturating the sheet material with adsorption in a foaming gas is performed at a pressure of 1.5 MPa-6 MPa for a time of 12-120 h.

[0015] In one embodiment, the foaming gas is selected from carbon dioxide, nitrogen, or air.

[0016] In one embodiment, the step of foaming the saturated sheet material in a foaming medium is carried out at a temperature of 90°C-220°C for a time of 10s-30s.

[0017] A polyethylene terephthalate foam material obtained by the preparation method described above, wherein the pore size of the polyethylene terephthalate foam material is 10μm-150μm and the expansion ratio is 2-20 times.

[0018] In the preparation method of this invention, the molten polyethylene terephthalate (PET) preform is subjected to melt isothermal crystallization treatment. This melt crystallization method induces PET to crystallize isothermally at a suitable temperature, resulting in the formation of microcrystalline regions within the obtained sheet material. This improves the melt strength of PET during the foaming process, enhances its foaming performance, and prevents phenomena such as cell rupture and aggregation. Simultaneously, the interface between the crystalline and amorphous regions can serve as heterogeneous nucleation sites, lowering the cell nucleation energy barrier and increasing the cell nucleation density. Therefore, the morphology of the foamed material can be controlled by enhancing cell nucleation and regulating cell growth.

[0019] Therefore, the preparation method of the present invention can obtain polyethylene terephthalate foamed materials with uniform cell size and controllable foaming ratio, which can be widely used in food packaging, household appliances, daily necessities, construction and transportation, automobile and aerospace industries and many other fields. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 Differential scanning calorimetry (DSC) curves of isothermal crystallization exothermic reaction of polyethylene terephthalate melt at different temperatures;

[0022] Figure 2 This is a cross-sectional cell morphology diagram of the polyethylene terephthalate foam material obtained in Example 1 of the present invention;

[0023] Figure 3 This is a cross-sectional cell morphology diagram of the polyethylene terephthalate foam material obtained in Example 2 of the present invention;

[0024] Figure 4 This is a cross-sectional cell morphology diagram of the polyethylene terephthalate foam material obtained in Example 4 of the present invention.

[0025] Figure 5 This is a cross-sectional cell morphology diagram of the polyethylene terephthalate sample obtained in Comparative Example 1 of the present invention.

[0026] Figure 6 This is a cross-sectional cell morphology diagram of the polyethylene terephthalate sample obtained in Comparative Example 2 of the present invention.

[0027] Figure 7This is a cross-sectional cell morphology diagram of the polyethylene terephthalate sample obtained in Comparative Example 3 of the present invention. Detailed Implementation

[0028] To facilitate understanding of the present invention, it will be described in more detail below. However, it should be understood that the present invention can be implemented in many different forms and is not limited to the embodiments or examples described herein. Rather, these embodiments or examples are provided to make the disclosure of the present invention more thorough and complete.

[0029] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments or examples only and is not intended to be limiting of the invention.

[0030] The method for preparing polyethylene terephthalate foam material provided by the present invention includes the following steps:

[0031] S1, hot-press the polyethylene terephthalate material to obtain a molten preform;

[0032] S2, the molten pre-product is subjected to melt isothermal crystallization treatment and quenching treatment to obtain sheet material;

[0033] S3, the sheet material is foamed to obtain polyethylene terephthalate foam material.

[0034] The crystallization process of polymers includes two stages: nucleus formation and grain growth. Crystallization by heating the polymer above its melting point and then rapidly cooling it from the molten state to a constant temperature is called isothermal melt crystallization. In the molten state, molecular chain segments form ordered bundles that act as nuclei through thermal motion. The orderly arrangement and regular stacking of these molecular chain segments towards the nuclei under constant temperature conditions allows for continuous grain growth.

[0035] Specifically, the regular symmetrical molecular chain structure of polyethylene terephthalate (PET) is conducive to crystallization, but the rigid benzene ring structure in its main chain restricts molecular chain movement. Therefore, its unique molecular chain structure allows for the control of the degree of crystallization perfection of PET through melt isothermal crystallization.

[0036] Therefore, in this invention, polyethylene terephthalate (PET) material is first made into a molten preform, and then the molten PET preform is subjected to melt isothermal crystallization treatment. The melt crystallization method induces PET to crystallize isothermally at a suitable temperature, resulting in the formation of tiny crystalline regions inside the sheet material. This can improve the melt strength of PET during the foaming process, enhance its foaming performance, and prevent phenomena such as cell rupture and agglomeration.

[0037] Meanwhile, the interface between crystalline and amorphous regions can serve as heterogeneous nucleation sites, reducing the nucleation energy barrier and increasing the nucleation density. This allows for the regulation of the cell morphology of foamed materials by enhancing cell nucleation and controlling cell growth, resulting in foamed materials with greater expansion ratios and more uniform cell structures.

[0038] Therefore, the preparation method of the present invention can obtain polyethylene terephthalate foamed materials with uniform cell size and controllable foaming ratio, which can be widely used in food packaging, household appliances, daily necessities, construction and transportation, automobile and aerospace industries and many other fields.

[0039] Specifically, intrinsic viscosity is an inherent characteristic of a polymer, closely related to its molecular weight, molecular weight distribution, and degree of branching. For polyethylene terephthalate (PET), a linear aromatic polyester, molecular weight is the primary factor influencing intrinsic viscosity; therefore, the higher the molecular weight, the higher the intrinsic viscosity. For the same polymer, under the same crystallization conditions, if the molecular weight is too high, the energy required for molecular chain segment movement is greater, resulting in poorer isothermal crystallization ability of the melt; conversely, if the molecular weight is too low, the crystallization rate is too fast, the degree of crystallization perfection is too sensitive to crystallization conditions, and the crystallization process is difficult to control.

[0040] Therefore, in order to better ensure the crystallization ability of polyethylene terephthalate, and thus to better control the crystallization process through melt isothermal crystallization and thus impart different degrees of crystallinity to the sheet material, in step S1, the intrinsic viscosity of the polyethylene terephthalate is 0.6 dL / g-0.8 dL / g.

[0041] In addition, depending on the application, polyethylene terephthalate (PET) can be divided into different grades. Currently, the two grades that dominate the market are fiber-grade PET and bottle-grade PET. Fiber-grade PET has an intrinsic viscosity of approximately 0.55 dL / g-0.67 dL / g and is commonly used in industrial spinning, while bottle-grade PET has an intrinsic viscosity of 0.75 dL / g-1.00 dL / g and can be used for food packaging. The intrinsic viscosity of polyethylene terephthalate used in step S1 of this invention is 0.6 dL / g-0.8 dL / g, which is lower than that of bottle-grade polyethylene terephthalate. Therefore, the isothermal melt crystallization method is used to induce the polyethylene terephthalate with a lower intrinsic viscosity to crystallize at a suitable temperature, so that tiny crystalline regions are formed inside the obtained sheet material, thereby improving the melt strength of polyethylene terephthalate during the foaming process and broadening the range of raw material options.

[0042] During isothermal crystallization of a melt, the crystallization rate, including the nucleation rate and the crystal growth rate, is highly temperature-dependent. At excessively high temperatures, the thermal motion of the molecular chains becomes too vigorous, making it difficult for crystal nuclei to form or resulting in unstable nuclei. As the temperature decreases, the nucleation rate increases, but the viscosity of the melt increases, reducing chain segment mobility and decreasing the crystal growth rate. Therefore, controlling the temperature during isothermal crystallization of a melt is crucial for controlling the crystallization process.

[0043] During isothermal crystallization of the melt, the nucleation process significantly affects the crystallization rate within a range of tens of degrees below the melting point. Lowering the crystallization temperature increases the crystallization rate and shortens the time required for complete crystallization. Therefore, within a suitable crystallization temperature range, the degree of crystallization perfection of polyethylene terephthalate can be controlled by either lowering the crystallization temperature while reducing the crystallization time, or by increasing the crystallization temperature while extending the annealing time.

[0044] The degree of crystallinity of polyethylene terephthalate (PET) has a significant impact on cell morphology. On the one hand, when the crystallinity is too low, it has little effect on melt strength, making it difficult for the cell walls to encapsulate gas, leading to cell rupture. On the other hand, excessive crystallinity reduces the solubility of gas in the polymer, increases matrix strength, and results in decreased cell density and size, even leading to a large number of unfoamed areas.

[0045] Figure 1 Differential scanning calorimetry (DSC) images of the isothermal crystallization exothermic reaction of polyethylene terephthalate (PET) melt at different temperatures are obtained from... Figure 1 It can be seen that as the isothermal crystallization temperature increases, the time required for crystallization to be completed increases, indicating that crystallization becomes more difficult and therefore requires a longer isothermal treatment time.

[0046] Therefore, taking into account the above factors, in the isothermal crystallization treatment of the melt described in step S2, the temperature is preferably 230℃-245℃ and the time is 3min-40min.

[0047] Furthermore, during the isothermal crystallization of the melt, pressure can be applied to prevent the melt from flowing freely, ensuring that the sheet material after isothermal crystallization has a good morphology. It should be noted that pressure has almost no effect on the isothermal crystallization process of the melt.

[0048] Furthermore, in the step of isothermal crystallization of the melt followed by quenching, the quenching medium is selected from ice water or liquid nitrogen to prevent the cooling process at room temperature from affecting the crystallinity inside the sheet material.

[0049] Furthermore, the thickness of the sheet material is preferably 0.5mm-3mm, so that when the sheet material is foamed, the foaming gas can diffuse better within the sheet material, shorten the saturation adsorption time, and at the same time, the escape rate of the foaming gas during the foaming process can be better controlled, ensuring that the cell size distribution of the foam material is uniform.

[0050] In actual operation, the specific process of steps S1 and S2 of the present invention can be as follows: provide a mold for preparing sheet material, place polyethylene terephthalate material in the mold in the form of granules, and then place the mold in a molding press to hot press into a sheet preform. At this time, the preform is in a molten state. Then, place the mold carrying the preform in another molding press for melt isothermal crystallization treatment. After isothermal crystallization treatment, quenching treatment is performed.

[0051] In step S3, the step of foaming the sheet material is as follows: the sheet material is saturated by adsorption in a foaming gas to obtain saturated sheet material, and then the saturated sheet material is foamed in a foaming medium.

[0052] Specifically, the foaming gas is selected from carbon dioxide, nitrogen, or air. Carbon dioxide can also play a plasticizing role in sheet materials, increasing the mobility of molecular chains, lowering the crystallization energy barrier, and helping to increase the crystallization density to obtain uniformly distributed cells. Therefore, the foaming gas is preferably carbon dioxide.

[0053] During the adsorption saturation process, when the foaming gas reaches a certain concentration, the plasticizing effect becomes too strong, which induces polyethylene terephthalate crystallization and produces a crystalline skin on the surface of the foaming material, affecting the uniform distribution of the pores. Therefore, in the step of adsorbing the sheet material into the foaming gas for saturation, the pressure is 1.5MPa-6MPa and the time is 12h-120h.

[0054] In the step of foaming the saturated system in a foaming medium, the foaming medium is selected from dimethyl silicone oil, glycerin, vegetable oil, machine oil or lubricating oil. The foaming medium, as a heat transfer medium, can transfer heat to the saturated sheet material to cause it to foam.

[0055] The foaming temperature provides the driving force required for cell growth during the foaming process, while the melt strength reflects the ability to resist cell rupture and coalescence during foaming. With increasing melt strength, polyethylene terephthalate (PET) can form a uniform cell structure even at higher foaming temperatures, without cell coalescence or rupture. Therefore, isothermal melt crystallization can improve the melt strength of PET during the foaming process, thereby broadening the foaming temperature range of PET. Therefore, in the step of foaming the saturated sheet material in the foaming medium, the preferred temperature is 90℃-220℃, and the preferred time is 10s-30s.

[0056] The present invention also provides a polyethylene terephthalate foam material obtained by the preparation method described above, wherein the pore size of the polyethylene terephthalate foam material is 10μm-150μm and the expansion ratio is 2-20 times.

[0057] Therefore, the apparatus and equipment used in the preparation method of this invention are all common equipment, such as molding machines and high-pressure autoclaves. The processing is easy to control, simple to operate, and has a short process. The foaming gas is used as a physical foaming agent, which has high solubility and diffusion coefficient compared with traditional chemical foaming agents. Moreover, it is a very environmentally friendly and green foaming system. This invention can adjust the cell morphology simply by changing the processing parameters. The production process is simple and has no impact on the performance and safety of the foamed material. It can be widely used in many fields such as food packaging, household appliances, daily necessities, construction and transportation, automobiles and aerospace industries.

[0058] The following specific embodiments will further illustrate the polyethylene terephthalate foam material and its preparation method.

[0059] Example 1:

[0060] Polyethylene terephthalate plastic granules (intrinsic viscosity of 0.7 dL / g) were placed in a vacuum oven and dried at 80°C for 12 hours to remove moisture from the plastic granules.

[0061] Polyethylene terephthalate (PET) plastic granules were placed in a mold with a thickness of 1 mm and molded for 5 minutes at a temperature of 280℃ and a pressure of 10 MPa to obtain a molten preform. The molten preform, along with the mold, was then quickly placed on another mold with a temperature of 232℃ for isothermal crystallization at a pressure of 10 MPa for 10 minutes. After isothermal crystallization, the melt, along with the mold, was quickly placed in an ice-water bath for quenching to obtain a sheet material with a thickness of 1 mm.

[0062] The obtained sheet material was placed in an autoclave and saturated with carbon dioxide gas. The pressure inside the autoclave was maintained at 4 MPa for 72 hours. Then, the pressure was rapidly released within 15 seconds, and the saturated sheet material was placed in dimethyl silicone oil at 150°C for 20 seconds to foam. Finally, the foamed sample was placed in ice water to fix the cell morphology, yielding polyethylene terephthalate foam material.

[0063] The cross-sectional scanning electron microscope image of the polyethylene terephthalate foam material obtained in this embodiment is shown below. Figure 2 As shown, from Figure 2 It can be seen that the sample is fully foamed and the cell size is uniform, with a cell size of 28.1 μm and an expansion ratio of 4.2 times.

[0064] Example 2:

[0065] The difference between Example 2 and Example 1 is that after obtaining the molten preform, the molten preform along with the mold is quickly placed on another molding press at a temperature of 235°C for isothermal crystallization of the melt, with a pressure of 10 MPa and an isothermal crystallization time of 10 min.

[0066] The cross-sectional scanning electron microscope image of the polyethylene terephthalate foam material obtained in this embodiment is shown below. Figure 3 As shown, from Figure 3 It can be seen that the sample is fully foamed and the cell size is uniform, with a cell size of 49.6 μm and an expansion ratio of 7.6 times.

[0067] Example 3:

[0068] The difference between Example 3 and Example 1 is that after obtaining the molten preform, the molten preform along with the mold is quickly placed on another molding press at a temperature of 237°C for isothermal crystallization of the melt, with a pressure of 10 MPa and an isothermal crystallization time of 10 min.

[0069] The polyethylene terephthalate foam material obtained in this embodiment is fully foamed with uniform cell size of 62.4 μm and an expansion ratio of 12.4 times.

[0070] Example 4:

[0071] The difference between Example 4 and Example 1 is that after obtaining the molten preform, the molten preform along with the mold is quickly placed on another molding press at a temperature of 240°C for isothermal crystallization of the melt, with a pressure of 10 MPa and an isothermal crystallization time of 10 min.

[0072] The cross-sectional scanning electron microscope image of the polyethylene terephthalate foam material obtained in this embodiment is shown below. Figure 4 As shown, from Figure 4 It can be seen that the sample is fully foamed and the cell size is uniform, with a cell size of 72.1 μm and an expansion ratio of 11.5 times.

[0073] Example 5:

[0074] The only difference between Example 5 and Example 1 is that the saturated sheet material was placed in dimethyl silicone oil at 180°C and foamed for 20 seconds.

[0075] The polyethylene terephthalate foam material obtained in this embodiment is fully foamed with uniform cell size of 37.2 μm and an expansion ratio of 5.4 times.

[0076] Example 6:

[0077] The only difference between Example 6 and Example 1 is that, during the process of placing the sheet material in an autoclave and introducing carbon dioxide gas for saturation treatment, the internal pressure of the autoclave is maintained at 3 MPa, the saturation time is 72 h, and then the pressure is quickly released within 15 s.

[0078] The polyethylene terephthalate foam material obtained in this embodiment is fully foamed with uniform cell size of 52.7 μm and an expansion ratio of 6.2 times.

[0079] Example 7:

[0080] The difference between Example 7 and Example 1 is that after obtaining the molten preform, the molten preform along with the mold is quickly placed on another molding press at a temperature of 232°C for isothermal crystallization of the melt, with a pressure of 10 MPa and an isothermal crystallization time of 5 min.

[0081] The polyethylene terephthalate foam material obtained in this embodiment is fully foamed with uniform cell size of 74.2 μm and an expansion ratio of 8.2 times.

[0082] Comparative Example 1:

[0083] The only difference between Comparative Example 1 and Example 1 is that the molten preform, along with the mold, was quickly placed in an ice-water bath for quenching.

[0084] The cross-sectional scanning electron microscope image of the polyethylene terephthalate foam material obtained in the comparative example is shown below. Figure 5 As shown, from Figure 5 It can be seen that the sample exhibits severe cell aggregation and cell wall rupture.

[0085] Comparative Example 2:

[0086] The only difference between Comparative Example 2 and Example 1 is that after obtaining the molten preform, the molten preform along with the mold is quickly placed on another molding press at a temperature of 220°C for isothermal crystallization of the melt, with a pressure of 10 MPa and an isothermal crystallization time of 10 min.

[0087] The cross-sectional scanning electron microscope image of the polyethylene terephthalate foam material obtained in the comparative example is shown below. Figure 6 As shown, from Figure 6 It can be seen that the sample cannot foam at all.

[0088] Comparative Example 3:

[0089] The only difference between Comparative Example 3 and Example 1 is that after obtaining the molten preform, the molten preform along with the mold is quickly placed on another molding press at a temperature of 225°C for isothermal crystallization of the melt, with a pressure of 10 MPa and an isothermal crystallization time of 10 min.

[0090] The cross-sectional scanning electron microscope image of the polyethylene terephthalate foam material obtained in the comparative example is shown below. Figure 7 As shown, from Figure 7 It can be seen that the sample contains a large number of unfoamed areas and the cell size distribution is uneven.

[0091] Comparative Example 4:

[0092] The only difference between Comparative Example 4 and Example 1 is that after obtaining the molten preform, the molten preform along with the mold is quickly placed on another molding press at a temperature of 250°C for isothermal crystallization of the melt, with a pressure of 10 MPa and an isothermal crystallization time of 10 min.

[0093] The polyethylene terephthalate foam material sample obtained in the comparative example exhibited severe cell aggregation and cell wall rupture.

[0094] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0095] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A method for preparing a polyethylene terephthalate foam material, characterized in that, Includes the following steps: Polyethylene terephthalate material is hot-pressed to obtain a molten preform; The molten preform is subjected to melt isothermal crystallization and quenching to obtain sheet material, wherein the melt isothermal crystallization temperature is 230℃-245℃ and the time is 3min-40min; and The sheet material is saturated by adsorption in a foaming gas to obtain a saturated sheet material. Then, the saturated sheet material is foamed in a foaming medium to obtain a polyethylene terephthalate foam material.

2. The method for preparing polyethylene terephthalate foam material according to claim 1, characterized in that, The intrinsic viscosity of the polyethylene terephthalate is 0.6 dL / g-0.8 dL / g.

3. The method for preparing polyethylene terephthalate foam material according to claim 1, characterized in that, In the quenching process, the quenching medium is selected from ice water or liquid nitrogen.

4. The method for preparing polyethylene terephthalate foam material according to claim 1, characterized in that, The thickness of the sheet material is 0.5mm-3mm.

5. The method for preparing polyethylene terephthalate foam material according to claim 1, characterized in that, In the step of saturating the sheet material with adsorption in a foaming gas, the pressure is 1.5MPa-6MPa and the time is 12h-120h.

6. The method for preparing polyethylene terephthalate foam material according to claim 1, characterized in that, The foaming gas is selected from carbon dioxide, nitrogen, or air.

7. The method for preparing polyethylene terephthalate foam material according to claim 1, characterized in that, In the step of foaming the saturated sheet material in a foaming medium, the temperature is 90℃-220℃ and the time is 10s-30s.

8. A polyethylene terephthalate foam material obtained by the preparation method according to any one of claims 1-7, characterized in that, The pore size of the polyethylene terephthalate foam material is 10μm-150μm, and the expansion ratio is 2-20 times.

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